This invention relates to a thread roll-forming machine and, more particularly, to an apparatus for forming tapered threads to a workpiece such as gas pipes and pipe fittings.
FIG. 1 shows a typical example of a conventional pipe or a pipe fitting, which has tapered screwthreads b formed at one open end a1 of a body a. Due to the fact that the tapered screwthreads b are formed by means of the threading dies, the one end a1 of the body a has a decreased thickness towards the opening end and since the material is removed away from the pipe, the effective strength of the screw heads may be adversely affected.
In the meantime, the tapered screwthreads b of the pipe body a shown in FIGS. 2 and 3 are produced by the rolling dies of a thread roll-forming machine. The screw threads b of the pipe of this type are usually formed by pressing the rolling dies without cutting the threads, so that the composition of the material will not be damaged and the effective strength of the screw heads is also not weakened. On the other hand, since a conventional thread roll-forming machine for pipes has a die supporting mechanism for supporting the rolling dies which is constructed so that a link mechanism and a cam mechanism are cooperative. This construction results in the increasing in the number of component parts, and complexity of the structure of the machine itself. Moreover, machine assembly and adjustment get complicated and maintenance time and labor are made troublesome. The machine becomes bulky as a whole structure which requires much space, thus being difficult to handle the same and to transfer the machine to a place for the installation thereof.